There is definite improvement in the shift points which is probably why it feels a little more snappy
. As far as actual horsepower, I'm not sure yet. Improved mileage has yet to be seen, although I must admit to stomping on it a little harder lately.
I was also told that there is a difference between the 03 and 04, but I would not worry about putting 104 octane boost in unless your getting some knocking. I ran through a half a tank of regular after programming to the performance tune and did not notice a knock. After the half tank I did start filling it with premium as suggested.